Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Re: GSM mobile phone
Posted: Fri Feb 26, 2010 12:18 pm
Joined: Sat Mar 04,
2006 10:12 am
The main two differences between any of the
telecom standards are the frequency bands of
operation and the modulation techniques. Some
use frequency modulation, others use phase
modulation, but all are some form of digital
modulation. Just as there are disparate groups
of auto enthusiasts that fervently believe their
choice of car is the best, groups exist in the
mobile communications cadres that think theirs
is the best. Some systems are better than other
form the standpoint of bandwidth efficiency, but
that often comes with a degradation in call
quality - particularly in weak signal
Take for example 16-QAM,
where the receiver must correctly discern 16
unique phase angle/amplitude combinations to
properly decode a data package. With a strong
signal and a slow-moving platform (a walking
talker), a phone can usually get near 100% of
the data packages without the need for error
correction or maybe have to request that the
packet be re-sent from the tower. Same goes in
the other direction from talker to tower.
Wne a user is moving quickly in a low power
enviroment with lots of signal interferes around
(electronics and physical), the system often
breaks down. That is because of ambiguity in
phase, amplitude. Take a simple BPSK signal in
the same environment that only needs to discern
between two separate states and it has a much
better chance of surviving. Problem is, though,
is that BPSK takes 8x the BW of a 16-PSK signal.
You can look up the technical difference
between the various mobil phone systems, but in
a nutshell this is the difference.